Brachiopods

Brachiopods have thrived in the world's
oceans for more than 550 million years and were especially common
before about 250 million years ago, since when the superficially
similar but unrelated bivalves have become the dominant shellfish
on the sea floor. Unlike bivalve molluscs, brachiopods are found
only in the sea. Most are filter-feeders living on the sea floor,
although a few types burrow into mud or sand.

Brachiopods are common fossils in Northern
Ireland, particularly in Carboniferous rocks (about 340 million
years ago) when some attained quite a large size (more than 150
mm across). Small brachiopods are not uncommmon near the base
of the Ulster White Limestone Formation (Upper Cretaceous) but
they are quite scarce in the Waterloo Mudstone Formation (Lower
Jurassic).